The present invention relates to a sputtering target and to methods of making the same.
Various sputtering techniques are used in order to affect the deposition of the film over the surface of the substrate. Deposited metal films, such as metal films on a thin film semiconductor device can be formed by a magnetron sputtering apparatus or other sputtering techniques. The magnetron sputtering apparatus induces plasma ions of a gas to bombard a target causing surface particles of the target material to be ejected therefrom, and to be deposited as a film or layer on the surface of a substrate. Conventionally, a sputtering source in the form of a planar disc or rectangle is used as the target, and ejected atoms travel along a line-of-sight trajectory to deposit on top of a wafer whose deposition face is parallel to the erosion face of the target. A hollow cathode magnetron (HCM) sputtering target in the shape of an inverted crucible or cup can be used as the target material. An inner chamber or sputtering cavity defined by the target contains a plasma that erodes the interior wall surfaces of the target in the manner mentioned above. An attribute of a sputtering system employing a hollow cathode target is its ability to deposit a film that is able to fill deep and narrow channels of the substrate. The above is accomplished when target atoms, ejected from the interior walls of the target, become ionized as they pass through the plasma. Magnetic fields then traject the ions in a direction perpendicular to the substrate.
DC magnetron sputtering or standard magnetron sputtering involves the well-known principles of “crossed-field” electrical gas discharges to give very high deposition rates, as well as other highly desirable parameters. The high deposition rates simply result from the fact that magnetically enhanced discharge plasmas allow very high power density under available conditions. With this technique, high deposition rates at low pressures are typical, and good uniformity and step coverage are possible. It is also possible to use RF (radio-frequency) alternating voltage instead of DC voltage in magnetron sputtering. A disadvantage of the above technique, however, is that the good deposition uniformity that it provides is brought about at the expense of very non-uniform erosion of the target. Thus, target life suffers.
Examples of sputtering devices and methods are described in U.S. Pat. No. 5,693,197 to Lal et al, U.S. Pat. No. 5,997,697 to Guenenfelder et al, U.S. Pat. No. 5,865,961 to Yokoyama et al, U.S. Pat. No. 5,855,745 to Manley, U.S. Pat. No. 6,033,536 to Ichihara et al, U.S. Pat. No. 5,529,674 to Hedgcoth, U.S. Pat. No. 5,656,138 to Scobey et al, U.S. Pat. No. 6,063,245 to Frach et al, U.S. Pat. No. 5,437,778 to Hedgcoth, U.S. Pat. No. 6,077,407 to Liehr et al, U.S. Pat. No. 5,770,025 to Kiyota, U.S. Pat. No. 5,188,717 to Broadbent et al, U.S. Pat. No. 5,171,415 to Miller et al, U.S. Pat. No. 6,083,364 to Ikeda et al, U.S. Pat. No. 3,884,793 to Penfold et al, and U.S. Pat. No. 5,393,398 to Sugano, all of which are incorporated herein by reference in their entireties.
Tantalum hollow cathode magnetron (HCM) sputtering targets are conventionally fabricated using crucibles that have been manufactured by welding and/or deep drawing. These techniques tend to impart metallurgical inhomogeneities to the cathode, which detrimentally impact sputtering performance. For example, weld beads and the surrounded heat-effected zone exhibit a grain structure and texture that differs from that of the bulk material. Such metallurgical inhomogeneities may create stray magnetic fields that impede the sputtering process. Likewise, deep drawing or spinning of annealed or stress-relieved plate may generate minor amounts of strain that are not uniformly distributed about the workpiece, resulting in a variable annealing response and/or sputtering erosion. Consequently, one of the disadvantages of HCM targets produced as described above is that they erode unevenly, resulting in a low number of acceptable wafers being produced from each tantalum HCM target due to a non-uniform deposition of target material on a substrate.
In designing the target and its associated magnetic field, two main objectives are a uniform erosion of the target and a uniform deposition of target material on the substrate.
Sputtering techniques that attempt to address the above objectives involve the use of rotating magnet DC magnetron sputtering, or of additional stationary components to be used in the sputtering device. The first mentioned technique addresses the question of material utilization efficiency by moving the magnet structure over the surface of the target in order to simultaneously obtain uniform material utilization and adequate step coverage. An example of the first technique is described in U.S. Pat. No. 5,770,025 to Kiyota, U.S. Pat. No. 5,188,717 to Broadbent et al, U.S. Pat. No. 5,171,415 to Miller et al, and U.S. Pat. No. 6,083,364 to Ikeda et al., all incorporated in their entirety herein by reference. An example of the second technique is described in U.S. Pat. No. 5,393,398 to Sugano, where a particle interceptor is disposed between the target and the substrate to yield a uniform deposited layer on the substrate. However, the above techniques are disadvantageous in that they involve the need to use complex and/or expensive equipment with a sputtering apparatus.
All the patents and publications mentioned above and throughout are incorporated in their entirety by reference herein.